Does the block need JavaScript, and does it work with full-page caching?

Yes, JavaScript must be enabled: the cookie is read and written, and the product cards are fetched over AJAX, entirely in the visitor's browser. Because the personalised list is loaded client-side after the page renders, the block stays correct per visitor even when the surrounding page is served from full-page or CDN cache. Nothing visitor-specific is baked into the cached HTML. If JavaScript is disabled the block simply stays hidden.